1. Field of the Invention
The present invention relates to a liquid crystal device comprising liquid crystal material, and more particularly to a liquid crystal device made by disposing transparent conductive films on the inner side surfaces of a pair of transparent substrates, respectively, and interposing containment means for containing the liquid crystal material in gaps between the transparent conductive films, thereby imparting a superior light modulating function to the liquid crystal device.
2. Description of the Prior Art
In an architectural or automotive application, the inflow of a solar radiation energy through a window exerts a large effect on a load of the air conditioning in the interior. Accordingly, in the viewpoint of energy saving, it becomes important to provide a light modulating function to the window.
As the light modulation range desired in practical use, it is necessary to select the optical characteristics at least in a range between the transparent glass used at present as a window glass and a heat absorbing glass for absorbing the solar radiation energy. The light modulation range is, preferably, within a range of 15% or more in terms of variable volume of the solar radiation energy transmittance (hereinafter, referred to as (".DELTA.T").
Conventionally, as a device having such light modulating function, there has been known an electrochromic device (hereinafter, referred to as "ECD"). The ECD functions to control the visibility and the transmitted light quantity of the solar radiation energy absorption of the light with the use of a material variable in the optical spectrum due to electrochemical oxidation-reduction reaction, such as tungsten oxide and prussian blue.
However, since the ECD is of current drive type, when being enlarged in area, it is remarkably reduced in a response time due to a large voltage drop and is inevitably degraded, for example, due to the electrochemical change of the elementary material in operating for a long period. Therefore, there has been not realized a large area device having a sufficient durability in practical use.
To solve the above problem, in place of the ECD of the above current drive type, there has been proposed a light modulating device of voltage drive type. Japanese Patent Laid-open No. sho 58-501631 corresponding to U.S. Pat. No. 4,435,047 discloses a nematic curvilinear aligned phase (hereinafter, referred to as "NCAP") liquid crystal device having a light modulating function being excellent in durability and easy in enlarging the area. Also, Japanese Patent Laid-open No. sho 60-502128 (U.S. Pat. No. 4,688,900) discloses a liquid crystal device obtained by a phase of separation method. These devices act on the basis of the following principle.
The liquid crystal device including tiny droplets of a liquid crystal material dispersed in a cheap polymer matrix looks milky white without applying voltage. This is because liquid crystals are aligned along with the curvilinear surface of a polymer wall, which distorts a light path or causes reflection and scattering of the light at each interface between the polymer matrix and the liquid crystals.
Meanwhile, in applying a voltage, the liquid crystals in the droplets are aligned parallel to direction of the electric field. In this case, by closing an ordinary refractive index of liquid crystals n.sub.o to be equal to a refractive index of polymer matrix n.sub.p, the incident light normal to the surface of a liquid crystal device passes through the interface of the polymer matrix and each liquid crystal without any reflection, thus making the liquid crystal device transparent.
The above liquid crystal device can control the visibility; however, since the incident light to the liquid crystal device is almost scattered on the opposed side (hereinafter, referred to as "forward") to the incident side in case of applying no voltage, the transmitted light quantity of the solar radiation energy is little reduced as compared with the case of applying voltage, thus obtaining only several % of .DELTA.T.
To solve the above problem, there has been proposed such a technique as disclosed in Japanese Patent laid-open sho 58-501631 (U.S. Pat. No. 4,435,047), wherein the absorption of the light in applying no voltage is increased by adding a pleochroic dye in a liquid crystal material used in the above liquid crystal device. Such a device has a large .DELTA.T; however, it cannot be used in the architectural or automotive application exposed in the solar radiation for a long period because the pleochroic dye is essentially easy to be degraded against the light and heat.